coils

[C.Pruysers]

With all the people in the know , it amazes me that nobody is willing to give us the specifications of existing coils . We have been so good in getting the schematics of commercial built detectors that it is unbelievable to assume that the specs of the coils are not available . Do we want to keep this info for ourselves or is it possible to exchange our knowledge with others . Some hobbyist we are if we don't share our knowledge with others . What do we gain by keeping it all for ourselves ? Kees

[Charles (NY)]

Re: coils

Step one is to get a good LCR meter and a scope and test 3-4 OEM coils for a machine to establish a range of variance for L, C, and R. Then you can start playing around with your own custom designs keeping within that range.

I just started winding coils for the Minelab Explorer and this stuff is akin to brewing a secret potion, each sized coil is a bit different.

I started with a custom 6 inch coil, only after experimentation did I arrive at the proper guage for the RX and TX. For my 6 inch coil 28 guage was right on for the RX and 22 guage for the TX. The turns were less important, regardles of guage you can get x inductance out of any given guage wire, its getting the correct inductance while staying within the variance range established also for C and R thats tricky. In this case 24 guage matched the TX inductance nicely but R was too high, R was too low using 20 guage.

On my latest coil, a 22 inch monster double D 28 guage was no good for the RX, R was too high, R was too low using 24 guage, 26 guage was right on.

Experimenting is half the fun though I have wasted some magnet wire in the process.

[C.Pruysers]

Re: coils

Charles . So good to hear your story . Ofcourse we all will get to the correct coil but sometimes we want to use the factory specs . I can tell you now that these can't be had ( as far as I know now ) . It is a fresh wind to hear from you and your escapades in winding coils . I too am experimenting with coils at the cost of a lot of wire . But hey ! It may be the only way to get the right coil . One thing I can tell you though and that is that whenever I find the right coil for certain detector , I will pass it on to the other hobbyists . For the time being , LETS KEEP TRYING . Regards Kees

[Carl]

Re: coils

Kees,

One problem is that metal detector schematics rarely include the coil winding info. Another is that reverse-engineering a detector is usually non-destructive, but with coils you have to split a sealed case and deal with epoxy, if you want # of turns, or to ID other passives.

I have measured coil inductances for a whole bunch of coils, and I have posted some of those from time-to-time. For DD coils, this is probably of good value. However, I question the value of TX inductance for concentric coils, because it includes the bucking coil. In other words, an TX coil measurement does not tell you the L of the actual TX coil, and the L of the bucking coil -- you get 'em both together.

I can post a big long list of coil inductances if you like. Like Charles mentioned, you really need several of each to get a good statistical distribution, but what I have is a good start.

Charles, I hope you will share more info on your Explorer coils. Sounds interesting!

- Carl

[C.Pruysers]

Re: coils

Carl Lets keep this movement going . It is clearly of great interest . Kees

[Jeff Kinzli]

Something to think about trying...

Carl, I agree with your comments about posting electrical parameters of coils, it would be of somewhat limited use for some coil designs.

On the other hand, I've been thinking of compiling a public coil parameters database. What I mean by this is creating a quick CGI script that would allow anyone with a coil and an LCR meter to post the characteristics of their coils. This would not only give us a wide range of data (who knows, it might open the door to finding coils that might work on other detectors without too much modification), but would also give us some insight into what kind of deviation there might be in manufacturer's production.

Of course all of this has a fairly high intrinsic error rate due to differences in measurement techniques, tools, round off errors, etc. but it might be interesting as an exercise to see what we get.

If anyone's interested post a followup or contact me off-forum. I can host the data collection and viewing on my website if need be, and if there's any appreciable interest.